1. Field of the Invention
An aspect of the present invention relates to a pattern forming method and a pattern forming apparatus.
2. Description of the Related Art
In the fabrication steps of semiconductor devices, in order to implement the processability and mass production of devices with fine patterns of 100 nm or below, for example, attention is focused on a nanoimprint lithography technique in which a patterned mold is brought into contact with a substrate such as a wafer for pattern transfer.
In the nanoimprinting method, an original plate (mold) having a pattern on one surface thereof is brought into contact with an imprinting material such as a resist layer coated on a substrate and the imprinting material is then cured, whereby the pattern is transferred.
For example, as the nanoimprinting method, the following methods are known: thermal imprinting methods using a thermoplastic resist disclosed in U.S. Pat. No. 5,772,905-B and JP-2003-77807-A, described later, and photo-imprinting methods using a photo-curing resist disclosed in JP-2001-68411-A and JP-2000-194142-A, described later.
As one example of the nanoimprinting method, the outline of a flow of pattern transfer according to a photo-imprinting method will be described.
The photo-imprinting method includes the following steps:                (1) applying a photo-curing resin onto a substrate,        (2) aligning a mold with a substrate and bringing them contact with each other,        (3) curing the resin with photoirradiation,        (4) removing the mold, and        (5) removing a remaining film.Here, in removing the remaining film, anisotropic etching with oxygen plasma has been mainly performed.        
In semiconductor lithography, by a demand for processing a base film after pattern formation, the height of a required pattern is defined. In photolithography, the height of the pattern after developed can be chiefly determined by the thickness of an applied resist film. In addition to this, although it is necessary to take into account of resist deformation caused by surface tension, for example, in developing and drying the resist, it is possible to satisfy the demand for processing the to-be-processed film in most cases.
However, in the nanoimprinting method, in the step of removing the mold contacted with the imprinting material on the substrate, it is necessary to remove the mold from the imprinting material in which the pattern is hardened.
Here, between the pattern and the mold, friction works depending on the contact area between them. The tensile strength of the imprinting material made of a resin becomes weakened as the width of the pattern becomes narrower.
Therefore, in the pattern with a narrow width and a high height, that is, in the pattern with a high aspect ratio, such a defect that the pattern may be broken when removing the mold.
In addition, when the adhesion between the imprinting material and the base substrate, or the adhesion of the individual interlayers in a multilayer structure of the base substrate is week, peelings may occur in the interface of the weakest adhesion.